With many devices, such as computers, redundant power supplies are provided. A redundant supply is understood to mean the presence of two functionally similar or comparable power supply units that are not simultaneously needed in the normal case. The redundant power supply is designed so that even in the case of a breakdown of one of the two power supply units, an interruption-free operation of the device can be guaranteed.
The power supply units are frequently designed so that an individual power supply unit can provide the peak electrical load of the system.
The result is that with a simultaneous operation, the two power supply units are operated with an individual output of a maximum 50%. Since power supply units, however, have a specific efficiency, which usually declines with an increasingly smaller electronic load, this mode of operation is very unfavorable for the energy consumption of the overall system.
This low efficiency can be avoided by having one of the two power supply units completely turned off during operation of the second power supply unit, that is, keeping one in the so-called “cold stand-by” mode. With a failure of the power supply unit in operation, one must switch over to the replacement power supply unit quickly enough to ensure uninterrupted operation. For this purpose, there must be a suitable electronic switch capable of switching, as quickly as possible, between the switched-off power supply unit and the one in operation. This also requires power supply units that are suitable for an operation of this type and provide for rapid switching. The disadvantage of this mode of operation is that the operating times of the two power supply units will be different. This leads to a different ageing as a result of the dissimilar wear of the two power supply units, and thus to an endangerment of the operating safety of the device.